I've seen similar. I live on a hill and the last quarter mile going home really dents my FE. And I can't get it back in the morning going down to the highway bec it's not warmed up yet. I thought maybe it was helping to FAS my way down the hill and warm up on the highway, but of course that doesn't balance out the loss on the way up. Haven't got an answer for gravity, at least as long as I insist on traveling around in a ton of metal.

Love my HAH.